1 / 49

Role of the central nervous system and endocrine glands in regulation of physiology functions

Role of the central nervous system and endocrine glands in regulation of physiology functions. The endocrine system. Notion about hormones. The endocrine system is composed of glands that secrete chemical signals into the circulatory system.

madra
Download Presentation

Role of the central nervous system and endocrine glands in regulation of physiology functions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Role of the central nervous system and endocrine glands in regulation of physiology functions

  2. The endocrine system

  3. Notion about hormones • The endocrine system is composed of glands that secretechemical signals into the circulatory system. • The secretory products of endocrine glands arecalled hormones (hoЇrmoЇnz), a term derived from the Greek wordhormon, meaning to set into motion. • Traditionally, a hormone is definedas a chemical signal, or ligand, that (1) is produced in minuteamounts by a collection of cells; (2) is secreted into the interstitialspaces; (3) enters the circulatory system, where it is transportedsome distance; and (4) acts on specific tissues called target tissues atanother site in the body to influence the activity of those tissues in aspecific fashion. All hormones exhibit most components of this definition,but some components don’t apply to every hormone.

  4. Hormone molecules diffuse from the blood through the walls of the capillariesinto the interstitial spaces. Once within the interstitial spaces, they diffuse tothe target cells. As the concentration of free hormone molecules increasesin the blood, more molecules diffuse from the capillary to the target cells. As the concentration of free hormone molecules decreases in the blood,fewer diffuse from the capillary to the target cells. Hormone Concentrations at the Target Cell

  5. Response of Target Cells to Hormones • (a) Down-regulation occurs when the number of receptors for a hormonedecreases within target cells. For example, gonadotropin-releasing hormone(GnRH) released from the hypothalamus binds to GnRH receptors in theanterior pituitary. GnRH bound to its receptors causes down-regulation of theGnRH receptors so that eventually the target cells become less sensitive to theGnRH. • (b) Up-regulation occurs when some stimulus causes the number ofreceptors for a hormone to increase within a target cell. For example, FSH actson cells of the ovary to up-regulate the number of receptors for LH. Thus theovary becomes more sensitive to the effect of LH.

  6. Some Hormones That Use the Adenylyl Cyclase–cAMPSecond Messenger System • Adrenocorticotropic hormone (ACTH) • Angiotensin II (epithelial cells) • Calcitonin • Catecholamines (b receptors) • Corticotropin-releasing hormone (CRH) • Follicle-stimulating hormone (FSH) • Glucagon • Human chorionic gonadotropin (HCG) • Luteinizing hormone (LH) • Parathyroid hormone (PTH) • Secretin • Somatostatin • Thyroid-stimulating hormone (TSH) • Vasopressin (V2 receptor, epithelial cells)

  7. Mechanisms of interaction oflipophilic hormones

  8. Some Hormones That Use the Phospholipase C SecondMessenger System • Angiotensin II (vascular smooth muscle) • Catecholamines (a receptors) • Gonadotropin-releasing hormone (GnRH) • Growth hormone–releasing hormone (GHRH) • Oxytocin • Thyroid-releasing hormone (TRH) • Vasopressin (V1 receptor, vascular smooth muscle)

  9. The Cascade EffectThe combination of a hormone with a membrane-bound receptor activates several G proteins. The G proteins, in turn, activate adenylyl cyclase enzymes, whichcause the synthesis of a large number of cAMP molecules. The cAMP molecules, in turn, activate many protein kinase enzymes, which produce a rapid andamplified response.

  10. Possible fates and actionsof a hormone followingitssecretion by anendocrine cell. Not allpaths apply to allhormones.

  11. Pathways by which the nervous system influences hormone secretion.(a) Certain neurons in the hypothalamus, some ofwhich terminate in the posterior pituitary, secrete hormones. The secretion of hypothalamic hormones from the posteriorpituitary and the effects of other hypothalamic hormones on the anterior pituitaryare described later in this chapter. (b) Theautonomic nervous system controls hormone secretion by the adrenal medulla and many other endocrine glands.

  12. Hypophysiotropic Hormones • Secretionof the anterior pituitary hormones is largelyregulated by hormones produced by the hypothalamusand collectively called hypophysiotropic hormones. • These hormones are secreted by neurons thatoriginate in diverse areas of the hypothalamus and terminatein the median eminence around the capillariesthat are the origins of the hypothalamo-pituitary portalvessels. • The generation of action potentials in theseneurons causes them to release their hormones, whichenter the capillaries and are carried by the hypothalamopituitaryportal vessels to the anterior pituitary. There they act upon the various anteriorpituitary cells to control their hormone secretions.

  13. Hypophysiotropic hormones • Each hypophysiotropic hormone is named for theanterior pituitary hormone whose secretion it controls. • Thus, secretion of ACTH (corticotropin) is stimulatedby corticotropin releasing hormone (CRH), secretionof growth hormone is stimulated by growth hormonereleasing hormone (GHRH), secretion of thyroidstimulatinghormone (thyrotropin) is stimulated bythyrotropin releasing hormone (TRH), and secretionof both luteinizing hormone and follicle-stimulatinghormone (the gonadotropins) is stimulated by gonadotropinreleasing hormone (GnRH).

  14. Neural Control of Hypophysiotropic Hormones • Neurons of the hypothalamus receive synaptic input,both stimulatory and inhibitory, from virtually all areasof the central nervous system, and specific neural pathwaysinfluence secretion of the individual hypophysiotropichormones. • A large number of neurotransmitters(for example, the catecholamines and serotonin) arereleased at the synapses on the hormone-secretinghypothalamic neurons, and this explains why the secretionof the hypophysiotropic hormones can be alteredby drugs that influence these neurotransmitters.

  15. Anterior pituitary

  16. Hypothalamic control of the posterior pituitary

  17. Anterior Pituitary Hormones • The anterior pituitary secretes at least eight hormones,but only six have well-established functions. • All peptides, these six “classical” hormones are folliclestimulatinghormone (FSH), luteinizing hormone(LH), growth hormone (GH), thyroid-stimulatinghormone (TSH, thyrotropin), prolactin, and adrenocorticotropichormone (ACTH, corticotropin). Each ofthe last four is probably secreted by a distinct cell typein the anterior pituitary, whereas FSH and LH, collectivelytermed gonadotropic hormones (or gonadotropins)because they stimulate the gonads, areboth secreted by the same cells.

  18. Section through an adrenal gland showing both the medulla and cortex, as well as the hormones they secrete.

  19. Hormonal Regulation of T3 & T4 Secretion 1. Thyroid-releasing hormone (TRH) is released from neurons inthe hypothalamus and travels in the blood to the anteriorpituitary gland. 2. TRH stimulates the release of thyroid-stimulating hormone(TSH) from the anterior pituitary gland. TSH travels in theblood to the thyroid gland. 3. TSH stimulates the secretion of thyroid hormones (T3 and T4)from the thyroid gland into the blood. 4. Thyroid hormones act on tissues to produce responses. 5. Thyroid hormones also have a negative-feedback effect on thehypothalamus and the anterior pituitary to inhibit both TRHsecretion and TSH secretion. The negative feedback helpskeep blood thyroid hormone levels within a narrow range.

  20. Positive feedback regulation of estrogen 1. During the menstrual cycle, before ovulation, smallamounts of estrogen are secreted from the ovary. 2. Estrogen stimulates the release of gonadotropin-releasinghormone (GnRH) from the hypothalamus and luteinizinghormone (LH) from the anterior pituitary. 3. GnRH also stimulates the release of LH from the anteriorpituitary. 4. LH causes the release of additional estrogen from theovary. The GnRH and LH levels in the blood increasebecause of this positive-feedback effect.

  21. Negative feedback regulation of estrogen 1. During the menstrual cycle, after ovulation, the ovarybegins to secrete progesterone in response to LH. 2. Progesterone inhibits the release of GnRH from thehypothalamus and LH from the anterior pituitary. 3. Decreased GnRH release from the hypothalamus reducesLH secretion from the anterior pituitary. GnRH and LHlevels in the blood decrease because of this negativefeedbackeffect.

  22. Gonadal production of steroids. Only the ovaries have highconcentrations of the enzymes (aromatase) required toproduce the estrogens estrone and estradiol.

  23. Aldosterone action

  24. Nervous & Endocrine System • Similarities: • They both monitor stimuli and react so as to maintain homeostasis. • Differences: • The NS is a rapid, fast-acting system whose effects do not always persevere. • The ES acts slower and its actions are usually much longer lasting.

More Related